There are three basic methods utilized in brewing coffee: (1) the Immersion method in which ground coffee beans are immersed in hot or boiling water, allowing sufficient dwell time for the coffee to "steep"; (2) the Regenerative or recycling method in which already brewed coffee is recycled through the coffee grounds to extract more flavor; and (3) the "once-through" drip method in which the water passes through the coffee grounds only once. Two types exist which use method #3; (a) those depending only on gravity to produce the flow through the coffee grounds and (b) the vacuum brewer in which condensing steam creates a vacuum to suck the water speedily through the coffee grounds. This method also permits the user to control the dwell time to extract the flavor without extracting excessive bitterness.
It is generally accepted by coffee brewing experts that, to obtain the best brew, the following conditions must be adhered to:
A. Coffee beans must be of high quality, properly roasted, and freshly ground or vacuum packed.
B. Brewing surfaces or components which come into contact with the water or the brewed coffee must be thoroughly cleansed to remove all traces of stale coffee. Preferably, such components should not be re-used.
C. Coffee should never be re-heated.
D. Brewing water should be boiling hot and kept hot by the use of insulated containers; delays in the brewing process permit the beverage to cool and are undesirable.
E. So far as possible, coffee "fines" or pulverized particles should be removed from the brewed beverage.
It is conceded also by brewing experts that the best coffee is that brewed by the "once-through" drip process if the water passes relatively quickly through the ground coffee, but this method, unfortunately, does not produce as high a yield as some other methods.
The oldest method of brewing coffee utilizes a coffee pot which is familiar to everyone because it is still in use in churches and the like. This device brews by the immersion method whereby water is brought to a boil in a pot, the ground coffee is added, the coffee is allowed to "steep" until it is strong enough, sometimes being boiled to speed the process and obtain a greater yield, and the finished brew is poured into a drinking vessel using a wire-mesh strainer to screen out the coarse particles of coffee. Unfortunately, a substantial amount of "fines" or pulverized particles ends up in the drinking vessel. Of course, this process produces an inferior beverage, but it is simple and quick, and involves a minimum of utensils, with maximum yield.
The percolator is an improvement over the coffee pot, involving the spraying of boiling water over a basket of coarse ground coffee, then reheating the brewed coffee and repeating the process to get the maximum yield. The boiling, however, gives the finished beverage a burnt flavor. Also, there are many components required and it is also impossible to remove all remnants of stale coffee.
The "once-through" drip method as exemplified by the "Dripolator" involves a three-part vessel, hot water being poured into the top vessel from whence it drips through a limited number of small holes into the middle vessel containing a measured amount of finely ground coffee and sometimes a filter, thence flowing through a great many holes into the bottom vessel. The process is slow, the "dwell" time is unpredictable, the brewer components are usually uninsulated with large surfaces exposed to cooling air, and it is impossible to remove all remnants of stale coffee.
The principal disadvantage of this method is that, being a "once-through" process, the coffee beans must be very finely ground to produce a satisfactory yield. This produces a variable amount of "fines" often depending on the condition of the coffee grinder. These fines fill in the spaces between the coarse particles and retards the progress of the water through the brewer, sometimes stopping it altogether. Because long immersion of the coffee grounds in water imparts a bitterness to the beverage, any delay in the brewing process is objectionable. This process relies on the weight of the water only to produce the flow through the ground coffee.
Various means of providing additional pressure to speed the flow have been suggested: complicated and costly pumps as in U.S. Pat. Nos. 1,089,900 and 1,754,146; steam pressure as in U.S. Pat. No. 3,589,272; and vacuum as in the Silex brewer. All of these involve a multiplicity of components which are difficult to thoroughly cleanse to remove all remnants of stale coffee which impair the taste of the beverage. The Silex is the only brewer of this type in current use and it is not adapted to the brewing of single servings.
Other brewers in current use utilize the "once-through" gravity method to produce a single serving, the best known of these being the Melitta brewer which consists of a funnel-shaped vessel with an integral flange to support the brewer on the lip of a drinking cup. A costly funnel-shaped filter is placed inside the funnel, a measured quantity of ground coffee is placed in the cone formed by the filter and boiling water is poured into the brewer. No guide marks are provided to indicate the amount of water in the vessel; hence, unless the water is premeasured, the resultant brew is variable in strength. Also, it is impossible to obtain the maximum yield from this method. The brewer is cumbersome and it is space-consuming to store many of them since they do not nest, each brewer requiring 110 cubic inches of storage space. Also, it is impossible to remove all of the stale coffee from the brewer. With coffee selling at $3.00 per pound and this brewer yielding about 45 cups to the pound, the coffee costs almost 7.cent. per cup which, added to the filter cost of 4.2.cent. each, make the cost of a cup of coffee about 11.cent..
There are other drip brewers in use, such as "Mr. Coffee", but these are costly and do not adapt to a single serving, although they are promoted for brewing 2 to 4 cups of coffee because of the recognition of the cost of brewing large portions of coffee when it is not all consumed. Restaurants and Diners use large drip brewers, but these use a cloth re-usable filter from which the stale coffee remnants cannot possibly be removed.
Because drip brewers in general rely on gravity flow of water through the brewer, they usually have a large diameter coffee compartment requiring a large diameter filter, and there is only a thin layer of ground coffee therein to reduce the resistance to the flow of the water. With this design, each drop of water passes through only a small thickness of grounds, resulting in a low yield from a given quantity of coffee beans. If the diameter were less, the stack would be higher and the yield would be greater.